cpusets, hotplug, scheduler: fix scheduler domain breakage
Commitf18f982ab
("sched: CPU hotplug events must not destroy scheduler domains created by the cpusets") introduced a hotplug-related problem as described below: Upon CPU_DOWN_PREPARE, update_sched_domains() -> detach_destroy_domains(&cpu_online_map) does the following: /* * Force a reinitialization of the sched domains hierarchy. The domains * and groups cannot be updated in place without racing with the balancing * code, so we temporarily attach all running cpus to the NULL domain * which will prevent rebalancing while the sched domains are recalculated. */ The sched-domains should be rebuilt when a CPU_DOWN ops. has been completed, effectively either upon CPU_DEAD{_FROZEN} (upon success) or CPU_DOWN_FAILED{_FROZEN} (upon failure -- restore the things to their initial state). That's what update_sched_domains() also does but only for !CPUSETS case. Withf18f982ab
, sched-domains' reinitialization is delegated to CPUSETS code: cpuset_handle_cpuhp() -> common_cpu_mem_hotplug_unplug() -> rebuild_sched_domains() Being called for CPU_UP_PREPARE and if its callback is called after update_sched_domains()), it just negates all the work done by update_sched_domains() -- i.e. a soon-to-be-offline cpu is included in the sched-domains and that makes it visible for the load-balancer while the CPU_DOWN ops. is in progress. __migrate_live_tasks() moves the tasks off a 'dead' cpu (it's already "offline" when this function is called). try_to_wake_up() is called for one of these tasks from another CPU -> the load-balancer (wake_idle()) picks up a "dead" CPU and places the task on it. Then e.g. BUG_ON(rq->nr_running) detects this a bit later -> oops. Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Tested-by: Vegard Nossum <vegard.nossum@gmail.com> Cc: Paul Menage <menage@google.com> Cc: Max Krasnyansky <maxk@qualcomm.com> Cc: Paul Jackson <pj@sgi.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: miaox@cn.fujitsu.com Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -1882,7 +1882,7 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
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* in order to minimize text size.
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*/
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static void common_cpu_mem_hotplug_unplug(void)
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static void common_cpu_mem_hotplug_unplug(int rebuild_sd)
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{
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cgroup_lock();
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@ -1894,7 +1894,8 @@ static void common_cpu_mem_hotplug_unplug(void)
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* Scheduler destroys domains on hotplug events.
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* Rebuild them based on the current settings.
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*/
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rebuild_sched_domains();
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if (rebuild_sd)
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rebuild_sched_domains();
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cgroup_unlock();
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}
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@ -1912,11 +1913,22 @@ static void common_cpu_mem_hotplug_unplug(void)
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static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
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unsigned long phase, void *unused_cpu)
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{
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if (phase == CPU_DYING || phase == CPU_DYING_FROZEN)
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switch (phase) {
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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case CPU_DOWN_FAILED:
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case CPU_DOWN_FAILED_FROZEN:
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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case CPU_DEAD:
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case CPU_DEAD_FROZEN:
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common_cpu_mem_hotplug_unplug(1);
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break;
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default:
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return NOTIFY_DONE;
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}
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common_cpu_mem_hotplug_unplug();
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return 0;
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return NOTIFY_OK;
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}
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#ifdef CONFIG_MEMORY_HOTPLUG
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@ -1929,7 +1941,7 @@ static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
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void cpuset_track_online_nodes(void)
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{
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common_cpu_mem_hotplug_unplug();
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common_cpu_mem_hotplug_unplug(0);
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}
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#endif
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